1. Field of the Invention
This invention relates generally to a dive computer for use by a user of a self-contained underwater breathing apparatus (SCUBA), and particularly to an advanced dive computer that calculates and displays the user""s breathing parameter, which is indicative of the rate at which air pressure is decreasing in the user""s compressed-air tank normalized with respect to the depth of the user.
2. Description of Related Art
Although sport diving can be fun, exciting and physically demanding, there are a variety of potential hazards that must be avoided. In particular, sport diving can be exceedingly dangerous if the diver becomes disoriented or light-headed. Thus, it is desirable for a diver to be able to monitor the rate at which he is consuming air. This task is complicated because the amount of air a diver actually breathes varies with depth even though the diver""s breathing rate remains unchanged. For example, if a diver consumes 20 psi per minute while breathing at a normal rate on the surface, he will consume 80 psi per minute if breathing at the same rate at a depth of 99 feet. Thus, for a diver to easily monitor his breathing rate, it is essential that the rate at which he is consuming air be normalized to eliminate the variable of depth.
There are several dive computers available today that display conventional dive parameters such as the amount of air pressure remaining in the user""s compressed-air tank, the depth of the user and in some instances the temperature of the surrounding water. Although display of these dive parameters provides the user with a xe2x80x9csnap-shotxe2x80x9d of his current conditions, they do not allow the user to monitor his rate of air consumption.
Accordingly, an object of the present invention is to provide a dive computer that calculates and displays the user""s breathing parameter, which is indicative of the rate at which air pressure in the user""s compressed-air tank is decreasing normalized with respect to the depth of the user. Another object of the present invention is to provide a method for calculating the user""s breathing parameter.
A diver""s breathing parameter is essentially a measure of his breathing efficiency. The more a person dives, the more efficient his breathing should become. Thus, another object of the present invention is to provide a dive computer that stores the diver""s breathing parameter in memory for later retrieval so that a diver can track his progress from dive to dive.
Since a diver will not normally stop breathing or suddenly triple his breathing rate, his breathing parameter will not normally go to either an extremely low or high level, and will not normally undergo rapid changes. Thus, a diver""s breathing parameter provides an indication of whether the diver is unduly stressed or in trouble and an indication of whether the diver""s equipment, including the dive computer itself, is operating correctly. Accordingly, another object of the present invention is to provide a dive computer that provides a visible warning and sounds an audible alarm when the diver""s breathing parameter either undergoes a rapid change or reaches an extremely low or high level.
These and other objects and advantages of the invention are accomplished by a dive computer for use by a user of a self contained underwater breathing apparatus. The dive computer includes a high pressure transducer for sensing air pressure in the user""s compressed-air tank, a low pressure transducer for sensing ambient pressure, a microcomputer coupled to each these transducers for calculating the user""s breathing parameter and a display coupled to the microcomputer for displaying the user""s breathing parameter. In accordance with the present invention, the transducers and microcomputer are included in a tank unit that is physically separate from the display, which is contained in a display unit. The invention may alternatively be assembled with the high pressure transducer in the tank unit and the low pressure transducer, the microcomputer and the display located in the display unit. Moreover, the invention may be assembled as a single unit.
The invention may also include an alarm circuit that sounds an audible alarm whenever the user""s breathing parameter either undergoes a rapid change or reaches an extremely high or low level.
The present invention provides a method for calculating a diver""s breathing parameter, which is indicative of the normalized rate at which air pressure in the diver""s compressed-air tank is decreasing. This method includes the steps of measuring air pressure in the user""s compressed-air tank and calculating the rate at which air pressure in the user""s compressed-air tank is decreasing. This method also includes measuring ambient pressure and calculating the depth of the user for each time interval for which air pressure in the user""s compressed-air tank is measured. In the preferred form, each of these measurements and calculations takes place once each second. From this information the user""s breathing parameter can be determined in accordance with the present invention by calculating the normalized rate at which air pressure in the user""s compressed-air tank is decreasing. This is accomplished by dividing the calculated rate at which air pressure in the compressed-air tank is decreasing by the depth of the user. Specifically the user""s instantaneous breathing parameter may be calculated according to the following:
In the preferred form the user""s instantaneous breathing parameter is averaged over a 64 second time span and then multiplied by 60 so that the actual breathing parameter displayed to the user is indicative of the rate at which air pressure in user""s compressed-air tank is decreasing in psi per minute, normalized for depth. The user""s actual breathing parameter is also stored in memory for later retrieval by the user.